1. Field of the Invention
The present invention relates to a magnetoresistance effect element for use in a magnetic head and the like.
2. Description of the Related Art
Generally, to read out information recorded in a magnetic recording medium, a reading magnetic head with a coil is moved relative to the recording medium, and a voltage induced in the coil by electromagnetic induction generated upon the movement is detected. A method using a magnetoresistance effect head to read out information is also known [IEEE MAG-7, 150 (1971)]. This magnetoresistance effect head makes use of a phenomenon in which the electrical resistance of a certain kind of a ferromagnetic substance changes according to the intensity of an external magnetic field, and is known as a high-sensitivity head for a magnetic recording medium. Recently, as magnetic recording media have been decreased in size and increased in capacity, the relative velocity between a reading magnetic head and a magnetic recording medium during information reading has decreased. Therefore, development of a magnetoresistance effect head capable of extracting a high output even at a low relative velocity has been desired increasingly.
Conventionally, an NiFe alloy (to be abbreviated as a permalloy hereinafter) has been used in a portion (to be referred to as an MR element hereinafter) of a magneto-resistance effect head in which the resistance changes in response to an external magnetic field. The permalloy, even one with good soft magnetic characteristics, has a maximum rate of change in magnetic resistance of about 3%, and this value is too low to use the permalloy as the MR element for a small-size, large-capacity magnetic recording medium. For this reason, a demand has arisen for an MR element material with a highly sensitive magnetic resistance change.
In recent years, it has been confirmed that a multilayered film formed by alternately stacking ferromagnetic metal films and nonmagnetic metal films, such as Fe/Cr or Co/Cu, under certain conditions, i.e., a so-called artificial lattice film gives rise to a very large change in magnetic resistance by using antiferromagnetic coupling between adjacent ferromagnetic films, and a film which exhibits a maximum rate of change in magnetic resistance exceeding 100% has been reported [Phys. Rev. Lett., Vol. 61, 2472 (1998)] [Phys. Rev. Lett. Vol. 64, 2304 (1990)].
Another type of a structure has also been reported, in which although ferromagnetic films do not experience antiferromagnetic coupling, an exchange bias is applied to one of two ferromagnetic films sandwiching a nonmagnetic film by using some means other than antiferromagnetic coupling between adjacent ferromagnetic films, thereby locking the magnetization of the film, which the magnetization of the other ferromagnetic film is reversed by an external magnetic field. This forms a state in which the two ferromagnetic films are antiparallel to each other on both the sides of the nonmagnetic film, realizing a large change in magnetic resistance. This type is herein termed a spin valve structure [Phys. Rev. B. Vol 45086 (1992)] [J. Appl., Phys., Vol. 69, 4774 (1991)].
In either of the artificial lattice film or the spin valve structure, the resistance change characteristics and the magnetic characteristics of the multilayered film change largely in accordance with the type of the ferromagnetic film. For example, in a spin valve structure using Co, such as Co/Cu/Co/FeMn, a high resistance change rate of 8% results, but the coercive force is as high as approximately 20 Oe, i.e., no good soft magnetic characteristics can be obtained. In contrast, in a spin valve structure using the permalloy, such as NiFe/Cu/NiFe/FeMn, although a good value of 1 Oe or less has been reported as the coercive force, the resistance change rate is not so high, about 4% [J. Al. Phys., Vol. 69, 4774 (1991)]. That is, the soft magnetic characteristics of the stacked film are good, but its resistance change rate decreases. Therefore, neither a constituent element nor a film structure of a stacked film which satisfies both the soft magnetic characteristics and the resistance change rate has been reported yet.
In addition, the above two types of the films have the following problems.
The artificial lattice film has a higher resistance change rate xcex94R/R (ignoring a magnetic field range) than that of the spin valve structure. However, a saturation magnetic field Hs of the artificial lattice film is large because antiferromagnetic coupling is strong, so the film suffers poor soft magnetic characteristics. In addition, since this RKKY-like antiferromagnetic coupling is sensitive to an interface structure, stable film formation is difficult to perform, and deterioration with time readily takes place.
A film with the spin valve structure can achieve good soft magnetic characteristics when an NiFe film is used as the ferromagnetic film. Since, however, the number of interfaces between the ferromagnetic films and the nonmagnetic film is two, the xcex94R/R is lower than that of the artificial lattice film. Even if a stacked film is constituted by ferromagnetic, nonmagnetic, and antiferromagnetic films in order to increase the number of interfaces, since the antiferromagnetic film with a high resistance is present in this stacked film, spin-dependent scattering is suppressed. Therefore, no increase in the xcex94R/R can be expected.
In addition, when a signal magnetic field is applied in the direction of the axis of hard magnetization of ferromagnetic films suitable for a magnetic head, the magnetization of only one of the ferromagnetic films is rotated. As shown in FIG. 1, therefore, the angle defined between the magnetization of a ferromagnetic film 2 on an antiferromagnetic film 1 and the magnetization of a ferromagnetic film 4 on a nonmagnetic film 3 can be changed to only about 90xc2x0 by the application of the signal magnetic field. Note that a change in the angle of up to 180xc2x0 occurs in the direction of the axis of easy magnetization. Consequently, the xcex94R/R decreases to about half that in the axis of easy magnetization. Assume, for example, that the exchange bias magnetic field of the ferromagnetic film 2 on the antiferromagnetic film 1 is weakened by some method to make it possible to use the magnetization rotations of both the ferromagnetic films 2 and 4. In this case, if the film thickness of the nonmagnetic film 3 is decreased to increase the resistance change rate, ferromagnetic coupling acts between the two ferromagnetic films. Therefore, the magnetization between the two ferromagnetic films point in the same direction when the signal magnetic field is 0. Consequently, even if the magnetizations rotate upon application of the signal magnetic field, only a slight change results in the angle between the magnetizations of the two ferromagnetic films, and so the resistance change is also subtle.
Furthermore, the ferromagnetic coupling acting between the two ferromagnetic films when the film thickness of the nonmagnetic film is decreased causes deterioration in permeability. The NiFe film having good soft magnetic characteristics has a normal anisotropic magnetoresistance effect. However, in a system in which a sense current is flowed in a direction perpendicular to a signal magnetic field, when the signal magnetic field is 0 and the magnetizations of two ferromagnetic films point in the same direction, but anisotropic magnetoresistance effect obtained by the signal magnetic field and the resistance change obtained by spin-dependent scattering cancel each other out, as shown in FIG. 2.
Common problems of the artificial lattice film and the spin valve structure will be described below. First, in order to obtain a high sensitivity in a magnetic head, a current to be supplied must be increased as large as possible. If the current is increased in either of the film structures, however, the magnetization directions of some ferromagnetic films are distributed by a magnetic field produced by this current, preventing a highly sensitive resistance change with respect to the magnetic field. More specifically, the magnetization readily points in the direction of the current magnetic field in the vicinities of the uppermost and lowermost layers of the stacked film, so the current magnetic field is strong in these portions.
Second, there are serious problems, such as the Barkhausen noise suppression and operating point bias, to be solved in applying the film to a magnetic head.
As described above, no existing magnetoresistance effect elements with the artificial lattice film or the spin valve structure using spin-dependent scattering can exhibit both good soft magnetic characteristics and a high resistance change rate xcex94R/R, which are essential to obtain a high sensitivity, even upon supply of a large current.
The present invention has been made in consideration of the above situation and has as its object to provide a magnetoresistance effect element which has a film with a spin valve structure or an artificial lattice film having good soft magnetic characteristics, and which can be applied to a high-sensitivity magnetic head.
In a magnetoresistance effect element which has a film with a spin valve structure or an artificial lattice film having good soft magnetic characteristics, and which can be applied to a high-sensitivity magnetic head, Co., CoFe, CoNi, NiFe, sendust, NiFeCo, Fe8N and the like may be used as a material of a ferromagnetic film. It is preferable that a thickness of the ferromagnetic film falls in the range of 1 to 20 nm. In the magnetoresistance effect element, a nonmagnetic metal such as Mn, Fe, Ni, Cu, AL, Pd, Pt, Rh, Ru, Ir, Au or Ag and an alloy such as CuPd, CrPt, CuAr, CuNi, as a material CuDi of a nonmagnetic film. It is preferable that a thickness of the nonmagnetic film falls in the range of 0.5 to 20 nm, more preferably 0.8 to 5 nm.
According to the first aspect of the present invention, there is provided a magnetoresistance effect element comprising a stacked film on a substrate by sequentially stacking a ferromagnetic film consisting primarily of at least one elements selected from the group consisting of Co, Fe, and Ni, a nonmagnetic film, and above ferromagnetic film, wherein the two ferromagnetic films are not coupled with each other, and the closest packed plane of each ferromagnetic film is oriented in a direction perpendicular to the film surface. In particular, it is desired that the ferromagnetic films made of Co1-xFex (0 less than xxe2x89xa60.4) exhibit high xcex94R/R and low Hc.
In the first aspect, xe2x80x9ctwo ferromagnetic films are not coupled with each otherxe2x80x9d means that essentially no antiferromagnetic films in other words antiparallel magnetization alignment must be stabilized by another method (e.g., to use of a bias film). The term xe2x80x9cclosest packed planexe2x80x9d means (111) plane for fcc phase, and (001) plane for hcp phase.
In the first aspect of the invention, the method of orienting the closest packed plane of the ferromagnetic film in the directing perpendicular to the film surface can be selected from: a method of adding to the material of the ferromagnetic film at least one element selected from the group consisting of Pd, Al, Cu, Ta, In, B, Nb, Hf, Mo, W, Re, Ru, Rh, Ga, Zr, Ir, Au, and Ag (of these elements, Pd, Cu, Au and Ag are particular desirable since they cause virtually no decrease in resistance change rate), a method of using the C face of a sapphire substrate as the substrate on which the ferromagnetic film is formed, and a method of forming, between the substrate and the ferromagnetic film, an undercoating film made of a material selected from the group consisting of material having fcc lattice, such as materials which fcc (face centered cubic) Bravais lattice of rhombohedral Bravais lattice (e.g., Cu Ni, CuNi, NiFe, NiO, Ge, Si, GaAs), Ti, a magnetic amorphous metal (e.g., CoZrNb, CoHfTa or the like), and a non-magnetic amorphous material.
More specific examples of the material of the above undercoating film are, when a ferromagnetic film having an fcc phase, such as a Co90Fe10 film, is used as the Co-based ferromagnetic film, a metal system having the fcc phase, such as a Cu-based alloy, such as Cuxe2x80x94Gexe2x80x94Zr, Cuxe2x80x94P, Cuxe2x80x94Pxe2x80x94Pd, Cuxe2x80x94Pdxe2x80x94Si, Cuxe2x80x94Sixe2x80x94Zr, Cuxe2x80x94Ti, Cuxe2x80x94Sn, Cuxe2x80x94Tixe2x80x94Zr, and Cuxe2x80x94Zr; an Au-based alloy, such as Auxe2x80x94Dy, Auxe2x80x94Pbxe2x80x94Sb, Auxe2x80x94Pdxe2x80x94Si, and Auxe2x80x94Yb; an Al-based alloy, such as Alxe2x80x94Cr, Alxe2x80x94Dy, Alxe2x80x94Gaxe2x80x94Mg, and Alxe2x80x94Si; a Pt-base allow a Pd-based alloy, such as Pdxe2x80x94Si and Pdxe2x80x94Zr, a Be-based alloy, such as Bexe2x80x94Ti, Bexe2x80x94Tixe2x80x94Zr, and Bexe2x80x94Zr; a Ge-based alloy, such as Gexe2x80x94Nb and Gexe2x80x94Pdxe2x80x94Se; an Ag-based alloy, an Rh-based alloy, an Mn-based alloy, an Ir-based alloy, and a Pb-based alloy; an alloy system consisting primarily of these metals having the fcc phase; a material having a diamond structure such as Ge, Si, and diamond; and a material having a zinc-blends structure, such as GaAs, Gaxe2x80x94Alxe2x80x94As, Gaxe2x80x94P, and Inxe2x80x94P. It is possible to use a material consisting primarily of at least one substance selected from these substances or a material formed by also adding other elements to any of these substances. Of the above materials, substances other than the single-element metal have an effect of suppressing the shunt current component because the substance themselves have specific resistances much higher than that of the ferromagnetic film. The increase in the specific resistance by the addition of other elements to the single-element metal can be obtained by various combinations. Examples are a Cu-based alloy, such as Cuxe2x80x94Ni, Cuxe2x80x94Cr, and Cuxe2x80x94Zr, and other alloys, such as Auxe2x80x94Cr, Fexe2x80x94Mn, Ptxe2x80x94Mn, and Nixe2x80x94Mn.
Examples of the nonmagnetic amorphous material are a nonmagnetic metal material, such as a nonmagnetic single-element metal or alloy and a material containing a non-metal as an additive, amorphous Si, such as hydrogenated Si, and a nonmagnetic nonmetallic material, such as amorphous carbon, e.g., hydrogenated carbon, glassy carbon, and graphite carbon.
The film thickness of the undercoating film is not particularly limited, but it is preferably 100 nm or less. This is so because even if the thickness of the undercoating film is increased to be larger than the above value, no larger effect can be obtained, and, conversely, the proportion of a current flowing through the undercoating film increases in the overall element, resulting in a decrease in resistance change rate. For nonmagnetic amorphous undercoating film, since it is possible to grow this undercoating film in the form of a layer of regardless of the type of the material of the substrate, a smooth surface can be obtained stably. In addition, the nonmagnetic amorphous undercoating film and hence has no adverse magnetic effect on the stacked film, i.e., the MR element which is formed on the undercoating film and in which the nonmagnetic film is interposed between the ferromagnetic films.
When the undercoating film is formed, it may have improved crystal orientation but may have a reduced surface smoothness and, hence, a decrease in the resistance change rate. Hence, it is desirable that the undercoating film be made of two films, the first of which improves crystal orientation in the closest packed plane, and the second of which is made of Ti, Ta, Zr or nonmagnetic amorphous metal for enhancing the plane smoothness and which is interposed between the first undercoating film and the substrate when the first undercoating layer is made of a material having fcc phase or magnetic amorphous metal. With this arrangement, there can be provided a magnetoresistance effect element having both good soft magnetic characteristics resulting from the improvement in the crystal orientation in the closest packed plane and the high rate of change in magnetic resistance. In addition, in this two-layered structure, the use of a second undercoating film having the same crystal system as that of the ferromagnetic film and consisting of a material having a higher specific resistance then that of the ferromagnetic film makes it possible to decrease the shunt current component of the current flowing through the element as well as achieving the above effect. When the undercoating film has a stacked structure of two or more layers, it is desirable that the film thickness of this stacked film do not exceed 100 nm.
As the method of forming the undercoating film as described above, it is possible to apply various film formation processes, such as a conventional sputtering process using RF discharge at 13.56 MHz, or 100 MHz or higher, ion beam sputtering processes using various ion sources, e.g., an ECR ion source and a Kaufman ion source, a vacuum deposition process using an electron beam evaporation source or a Knudesen cell, a thermal CVD process, CVD processes using various plasmas, and an MOCVD process or an MOMBE process using an organometallic compound as a material. It is important in all of these film formation processes to control water and oxygen by evacuation of up to an ultra-high vacuum and realization of a very high purity of a material gas. More specifically, the contents of H2O and O2 are reduced to preferably the order of ppm or less, and more preferably the ppb order.
In the first aspect of the invention, the material of the ferromagnetic film contains as its main constituents at least one elements selected from the group consisting of Co, Fe, and Ni. In particular, Co100-xFex (5xe2x89xa6Xxe2x89xa60.4) is preferred. This is so because it can readily achieve low Hc and high resistance change, while magnetic film without Co does not show much higher xcex94R/R than NiFe films and magnetic films composed of only Co dose not show the remarkable improvement of the soft magnetic properties, such as low Hc, because of large crystal magnetic anisotropy regardless of the closest packed plane orientation.
As for the crystal orientation of the ferromagnetic film, a half-width of a rocking curve of a reflection peak of a (111) plane, as the closest packed plane, in an X-ray diffraction curve is preferably less than 20xc2x0, and most preferably 7xc2x0 or less.
Representative examples of the substrate material are a single-crystal substance, such as MgO, sapphire, diamond, graphite, silicon, germanium, SiC, BN, SiN, AlN, BeO, GaAs, GaInP, GaAlAs, and BP, a polycrystalline substance of any of these single-crystal substances, a sintered body containing any of these single-crystal substances as its main constituent; and a single-crystal substance, as polycrystalline substance, and a sintered body of magnetic or nonmagnetic metal. The substrate material is selected in accordance with the type of the ferromagnetic film and the material of the undercoating film. Use of the C face of a sapphire substrate as the substrate is most preferable because it is well lattice-matched with Co-based magnetic film and likely to have a smooth surface. When a single-crystal substrate, such as a sapphire substrate, is used, the thickness of the ferromagnetic film is preferably 20 nm or less. This is so because if the thickness of the ferromagnetic film exceeds 20 nm, the (111) orientation is degraded.
In the magnetic film which is (111)-oriented, Hc increases abruptly when the magnetization direction inclines slightly from the (111) plane. Therefore, even if the (111) orientation is realized, the magnetization direction sometimes falls outside the range of the (111) plane, so Hc does not decrease if undulations are present on the substrate surface. For this reason, the surface roughness of the substrate is preferably less than 5 mm.
Note that the arrangement of the magnetoresistance effect element of the first aspect is not limited to the above arrangement but may be one formed by alternately stacking nonmagnetic films and ferromagnetic films a plurality of number of times.
The second aspect of the present invention provides a magnetoresistance effect element comprising a stacked film formed on the substrate by sequentially stacking a ferromagnetic film consisting primarily of at least one element selected from the group consisting of Co, Fe, and Ni, a nonmagnetic film, and above ferromagnetic film, wherein the material of the ferromagnetic film contains at least one element selected from the group consisting of Pd, Al, Cu, Ta, In, B, Nb, Hf, Mo, W, Re, Ru, Rh, Ga, Zr, Ir, Au, and Ag. Of these elements which cause virtually no decrease in resistance change rate are particularly desirable for three reasons. First, they do not form an intermetallic compound. Second, the ferromagnetic film will be lattice-matched well with the intermediate nonmagnetic film (Cu or the like). Third, large spin-dependent scattering can be expected to occur due to so-called xe2x80x9cbulk scatteringxe2x80x9d. In the second aspect, a content of the additional element is set within the range in which a CoFe alloy exhibit a ferromagnetic property at room temperature. For example, it is preferable that a content of the additional element is less than 6.5 at % in a case of Al, Ga, or In, that a content of the additional element is less than 10 at % in a case of Nb, Ta, Zr, Hf, B, Mo, or W, and that a content of the additional element is less than 40 at % in a case of Cu, Pd, Au, Ag, Re, Ru, Rh, or Ir.
The arrangement of the magnetoresistance effect element of the second aspect of the invention is not limited to the above arrangement but may be one formed by alternately stacking nonmagnetic films and ferromagnetic films a plurality of number of times.
The third aspect of the present invention provides a magnetoresistance effect element comprising a stacked film formed on a substrate by sequentially stacking a ferromagnetic film, a nonmagnetic film and another ferromagnetic film, wherein each ferromagnetic film is comprised of five or less layers, a ferromagnetic film having a resistivity of 50 xcexcxcexa9xc2x7cm or more is formed on upper layer of the stacked film and/or between the substrate and lower layer of the stacked film.
In the third aspect, the high-resistance magnetic film means a ferromagnetic film or a magnetic film having ferromagnetism. In addition, the ferromagnetic film is limited to the stacked film constituted by five or less layers. This is because, if the interface between the ferromagnetic film and the nonmagnetic film increases, the interface between the high-resistance magnetic film and the ferromagnetic film become less active, failing to the effect of the increase in the ratio xcex94R/R.
By stacking the films such that the high-resistance magnetic film is in contact with the ferromagnetic film, occurrence of magnons in the interface can be prevented. If, however, the resistivity of the material of this high-resistance magnetic film is less than 50 xcexcxcexa9xc2x7cm, a current flows mainly through the high-resistance magnetic film, undesirably decreasing the resistance change rate. In other words, it is possible to prevent the current from being shunted to the high-resistance magnetic film by using a ferromagnetic film or a magnetic film having ferromagnetism which has a resistivity of 50 xcexcxcexa9xc2x7cm or more.
As a material of the high-resistance magnetic film, Ni, Fe, Co, NiFe, NiFeCo, CoFe, Co-based alloy, containing an additional element such as It, V, Cr, Mn, Zn, Nb, Tc, Hf, Ta, W, Re, and the like may be used.
In the third aspect, the high-resistance magnetic film is preferably a high-resistance soft magnetic film. As the high-resistance soft magnetic film, it is possible to use a high-resistance amorphous film consisting of, e.g., CoZrNb, a fine-crystal high-resistance soft magnetic film consisting of, e.g., FeZrN or CoZrN, or a film consisting of a material in which X of NiFeX is one element selected from the group consisting of Rh, Nb, Zr, Hf, Ta, Re, Ir, Pd, Pt, Cu, Mo, Mn, W, Ti, Cr, Au, and Ag. Of these films, the amorphous film or the film consisting of the material consisting of CoZrN or NiFeNb and having an fcc phase is desirable because the film promotes the fcc (111) orientation of the ferromagnetic film formed on it.
The film thickness of the high-resistance magnetic film preferably ranges between 0.5 nm or more. This is because if the film thickness is less than 0.5 nm, the magnetism of the high-resistance magnetic film itself is weakened to make prevention of occurrence of magnons difficult. In the case where the high-resistance magnetic film is inferior to the adjacent ferromagnetic film in terms of soft magnetic characteristics, it desirably has a thickness of 10 nm or less. This is because a film thickness exceeding 10 nm has an influence on the magnetization process of the ferromagnetic film, and this makes it difficult to obtain soft magnetic characteristics.
In the third aspect of the invention, usable examples of the material of the ferromagnetic film are Co, CoNi, CoFe, NiFe, and NiFeCo. The film thickness of the ferromagnetic film preferably ranges from 1 to 20 nm.
In the third aspect, the high-resistance magnetic film can be formed as the uppermost layer.
The arrangement of the magnetoresistance effect element according to the third invention is not limited to the above arrangement but may be one formed by alternately stacking nonmagnetic films and ferromagnetic films five times or less. The magnetoresistance effect element of the third invention is also suitable for the spin valve structure.
The fourth aspect of the present invention provides a magnetoresistance effect element comprising a stacked film formed on a substrate by sequentially stacking a ferromagnetic film, a first nonmagnetic film and another ferromagnetic film, wherein each ferromagnetic film is comprised of five or less layers, a second nonmagnetic film having a resistivity twice or less that of the ferromagnetic film is formed on upper layer of the stacked film and/or between the substrate and lower layer of the stacked film, and the magnetic film in contact with the second nonmagnetic film has a thickness of less than 5 nm.
In the fourth aspect, the material of the second nonmagnetic film preferably has the same crystal structure as that of the material of the ferromagnetic film (e.g., when the ferromagnetic film consists of a material having the fcc phase, the first nonmagnetic film also consists of a material having the fcc phase). In this case, it is preferable that the difference in lattice constant between the material of the second nonmagnetic film and the material of the ferromagnetic film be 5% or less. This is so because the ferromagnetic film can be epitaxially grown by increasing the crystal matching properties between the ferromagnetic film and the second nonmagnetic film, and this can suppress scattering of electrons in the interface.
In the fourth aspect, as the material of the second nonmagnetic film, it is possible to use a material consisting primarily of at least one element selected form the group consisting of Mn, Fe, Ni, Cu, Al, Pd, Pt, Rh, Ir, Au, and Ag. It is also possible to interpose a second undercoating film between the substrate and the second nonmagnetic film. Cu, Ag, Au, CuPd, CuPt, CuAu, or CuNi may be used as a material of the first nonmagnetic film. It is preferable that a thickness of the first nonmagnetic film falls the range of 0.5 to 20 nm.
In the fourth invention, when two or more ferromagnetic films are present, it is desirable that the grain size of the crystal of the material constituting the ferromagnetic films be large in the direction of the film thickness so as not to interfere with crystal growth in each ferromagnetic film. If the ferromagnetic film is constitute by six or more, the spin-dependent scattering interface increases, and the advantage of the invention will not be attained in effect.
The film thickness of the second nonmagnetic film preferably ranges between 0.2 and 20 nm. If the film thickness of the second nonmagnetic film is less than 0.2 nm, a probability that electrons flowing into the second nonmagnetic film undergo inelastic scattering in the interface with the substrate increases, and this makes it difficult to effectively extend the mean free path. If, on the other hand, the film thickness exceeds 20 nm, no larger effect can be obtained, and a current flowing only through the second nonmagnetic film increases to make it difficult to obtain a high change rate.
In the spin valve type magnetoresistance effect element according to the fourth aspect, the nonmagnetic film is so stacked as to contact at least the ferromagnetic film whose magnetization is not locked by the antiferromagnetic film. By stacking the nonmagnetic film in contact with the ferromagnetic film, electrons flow into the nonmagnetic film even if the thickness of the ferromagnetic film is less than 5 nm, and this can keep the effective mean free path of electrons long.
When the magnetoresistance effect element of the fourth aspect of the invention is applied to a sensor, the material of the first nonmagnetic film has a resistivity preferably twice or less, and more preferably lower that of a CoFe alloy as the material of the ferromagnetic film for the reason explained below. That is, if the bulk resistivity of the first non-magnetic film is significantly higher than that of the ferromagnetic film, electrons flowing into the nonmagnetic film undergo scattering, and consequently the effective mean free path can no longer be kept long.
The resistivity of the material of the first nonmagnetic film is preferably xc2xc or more the resistivity of the ferromagnetic film, since if the resistivity of the material of the second nonmagnetic film is less than xc2xc the resistivity of the ferromagnetic film, a current easily flows into the second nonmagnetic film.
In the fourth aspect, the first nonmagnetic film may be formed as the uppermost layer.
The arrangement of the magnetoresistance effect element of the fourth aspect is not limited to the above arrangement but may be one formed by alternately stacking second nonmagnetic films and ferromagnetic films a plurality of number of times. In addition, the magnetoresistance effect element of the fourth invention can have either the spin valve structure or the artificial lattice film structure.
The fifth aspect of the present invention provides a magnetoresistance effect element comprising a stacked film formed on a substrate by sequentially stacking a ferromagnetic film, a nonmagnetic film, and another ferromagnetic film, and a thin film formed on upper layer of the stacked film and/or between the substrate and lower layer of the stacked film, and having a resistivity higher than that of the ferromagnetic film and a mean free path longer than that of the ferromagnetic film.
In the fifth aspect, examples of the material of the thin film are a semimetal, such as Bi, Sb, and carbon, a semiconductor degenerated by doping at a high concentration, and an oxide semiconductor, such as SnO2 and TiO2. The film thickness of the thin film is preferably 1 to 50 nm for the reason explained below. That is, if the film thickness of the thin film is less than 1 nm, the effect of increasing the mean free path of electrons cannot be obtained satisfactorily. If the film thickness exceeds 50 nm, on the other hand, no larger effect can be obtained, and a current flowing through the thin film increases to make it difficult to obtain a high change rate.
In the fifth invention, the mean free path means the average of the distances electrons travel without scattered by any other thin.
In the fifth aspect, if the resistivity of the thin film is lower than that of the ferromagnetic film, a current flows into the thin film, weakening the magnetoresistance effect. Therefore, the thin film is formed to have a resistivity higher than that of the ferromagnetic film.
In the fifth aspect, in order to increase the resistivity of the entire stacked film, the film thickness of ferromagnetic film in contact with the thin film is set at preferably 5 nm or less, whereas the film thickness of the ferromagnetic film not in contact with the thin film is set to fall within the range of 2 to 20 nm in order to keep a required mean free path.
The arrangement of the magnetoresistance effect element of the fifth aspect is not limited to the above arrangement but may be one formed by alternately stacking nonmagnetic films and ferromagnetic films a plurality of number of times.
The sixth aspect of the present invention provides a magnetoresistance effect element comparison an undercoating film formed on a substrate and having the fcc phase, and a stacked film obtained by sequentially stacking a ferromagnetic film formed on the undercoating film and consisting of a CoFe alloy, a nonmagnetic film, and another ferromagnetic film, wherein the undercoating film consists of a material with a larger lattice constant than that of the material of the ferromagnetic film.
Note that no decrease in Hc was found when a Co film was formed on a glass substrate via a Cu undercoating film. This indicates that the effect of improving soft magnetism using an undercoating film is achieved when a ferromagnetic film consists of an alloy obtained by adding Fe to Co. It was found that a low Hc was realized especially when the concentration of Fe to be added to Co was 5% to 40%. This is so because if the Fe concentration is less than 5%, the hcp phase is mixed, and, if the Fe concentration exceeds 40%, the bcc phase is mixed easily and the lattice mismatching occurs. Examples of elements to be added to CoFe are Ni, Pd, Al, Cu, Ta, In, B, Zr, Nb, Hf, Mo, W, Re, Ru, Ir, Rh, Ga, Au, and Ag. The Hc reducing effect can be achieved similarly when these elements were added.
In the sixth aspect of the invention, the undercoating film preferably consists of a material with a higher resistivity than that of the CoFe alloy constituting the ferromagnetic film. It is also preferable that a film for improving smoothness be formed between the substrate and the undercoating film. As the film for improving smoothness, a film consisting of, e.g., Cr, Ta, Zr, Ti or the like can be used.
It is also preferable that the undercoating film thickness is less than 20 nm because the sense current in the undercoating film can keep small.
Note that the arrangement of the magnetoresistance effect element according to the sixth invention is not limited to the above arrangement but may be one formed by alternately stacking nonmagnetic films and ferromagnetic films a plurality of number of times.
The seventh aspect of the present invention provides a magnetoresistance effect element comprising a unit stacked film formed on a substrate and constituted by (a first ferromagnetic film/a first nonmagnetic film)n (nxe2x89xa71)/a first ferromagnetic film, and a second ferromagnetic film formed on the unit stacked film via a second nonmagnetic film having a thickness different from that of the first nonmagnetic film, wherein the magnetizations of the individual ferromagnetic films of the unit stacked film are ferromagnetically coupled with each other. The second ferromagnetic film may be above unit stacked film or may be single layered ferromagnetic film.
In the seventh aspect, the first nonmagnetic film of the unit stacked film preferably has a thickness of 2 nm or less, by which no RKKY-like antiferromagnetic coupling is caused, since the magnetizations of the individual ferromagnetic films in the unit stacked film can be kept in a ferromagnetically coupled state. As an example, if the material of the ferromagnetic film is CoFe and the material of the first nonmagnetic film is Cu, the thickness of the first nonmagnetic film is set at a value not in the vicinity of 1 nm. It is preferable that a thickness of the second nonmagnetic film falls the range of 0.5 to 20 nm.
In addition, it is desirable that the ferromagnetic film and the first nonmagnetic film the grown while maintaining the lattice matching, i.e., the ferromagnetic film and the nonmagnetic film be lattice-matched to cause no excess scattering in the interface between them. This can prevent an increase in the resistance.
Note that the arrangement of the magnetoresistance effect element of the seventh aspect is not limited to the above arrangement but may be one formed by alternately stacking nonmagnetic films and ferromagnetic films a plurality of number of times. Note also that the magnetoresistance effect element of the seventh aspect is applicable to both the spin valve structure and the artificial lattice film structure.
The eighth aspect of the present invention provides a magnetoresistance effect element comprising a stacked film formed on a substrate by sequentially stacking a ferromagnetic film, a nonmagnetic film, and another ferromagnetic film, wherein each of magnetization of two adjacent ferromagnetic films is rotated in the reverse direction each other when a bias magnetic field in the reverse direction is applied to each of two ferromagnetic films by using a bias magnetic film as at least one bias magnetic field.
In the eighth aspect of the invention, the method of applying the bias magnetic fields to cause the each magnetization direction of the two ferromagnetic films to rotate in the reverse direction can be used a method using exchange coupling from an antiferromagnetic film and also using a hard magnetic film, or a method using an exchange bias produced by stacking a ferromagnetic film onto the ferromagnetic film in the stacked film as a biasing means to be applied to one ferromagnetic films and can be used a method using a bias magnetic field generated by a current, static coupling (a demagnetizing field) generated when a fine pattern is processed as a biasing means to be applied to another ferromagnetic film.
More specifically, antiferromagnetic films are stacked on the individual ferromagnetic films, and the ferromagnetic films are magnetized by using the antiferromagnetic films in a way which produces a difference of 180xc2x0 in the direction of the bias magnetic field between the two adjacent ferromagnetic films. This magnetization can be achieved by, e.g., a method in which the direction of the application of the static magnetic field in the formation of the antiferromagnetic films is changed by 180xc2x0 from that in the formation of the ferromagnetic films. In this case, it is desirable that the magnitude of the bias magnetic field to be applied to the neighboring ferromagnetic films be a minimum value required to form a single domain in the ferromagnetic film, e.g., 5 kA/m or less. In addition, the two antiferromagnetic films preferably have different Neel temperature in order to easily apply a bias magnetic field in different direction each other to each of ferromagnetic film.
The following method is also usable as an alternative. That is, an exchange bias magnetic field generated by stacking the antiferromagnetic film is used in application of the bias magnetic field to one ferromagnetic film. In application of the bias magnetic field to the other ferromagnetic film, another ferromagnetic film is stacked on the remaining film surface of the antiferromagnetic film, and a static coupled magnetic field (a demagnetizing field) generated when this ferromagnetic film whose magnetization is locked by the antiferromagnetic films formed into a fine pattern is used. This new ferromagnetic film preferably has a two-layered structure formed by stacking a ferromagnetic film A (e.g., a film consisting of a material with a high crystallinity, such as NiFe or CoFe) suitable for application of the exchange bias, on the side in contact with the antiferromagnetic film, and a ferromagnetic film B (e.g., a Co-based amorphous ferromagnetic film or a nitride or carbide fine-crystal ferromagnetic film) suitable for generating the static coupled magnetic field onto the ferromagnetic film A, so as to cause ferromagnetic exchange coupling between them. With this two-layered structure, it is possible to adjust the Bs or the resistance (e.g., to increase the Bs and increase the resistance) of the ferromagnetic film B by controlling the film thickness, the composition, and the formation conditions of the ferromagnetic film B, thereby adjusting the strength of the static coupled bias magnetic filed or a shunt bias (operating point bias) generated when a portion of a sense current flows through the ferromagnetic films B. When using NiFe films with the anisotropic magnetoresistance as a ferromagnetic film it is preferable that a sense current is made to flow in a direction perpendicular to a direction of a signal current.
In applying a bias magnetic field to a ferromagnetic film by using an antiferromagnetic film, a problem arises if the bias magnetic field is too large. However, this large bias magnetic field can be decreased by interposing, between the antiferromagnetic film and the ferromagnetic film, a stacked film of a ferromagnetic film and a non-magnetic film in which the ferromagnetic film is present on the antiferromagnetic film side.
In the conventional spin valve film, if the nonmagnetic film is 2 nm or less thick, the ferromagnetic coupling between the ferromagnetic films spaced apart by the nonmagnetic film is strengthened, making it no longer possible to antiparallel magnetization alignment. Nonetheless, in the eighth aspect of the present invention, the bias magnetic field can be strengthened more than the ferromagnetic coupling field described above even if the nonmagnetic film has a thickness of 2 nm or less. As a result, the antiparallel magnetization alignment can be achieved. The spin valve can obtain a higher xcex94R/R than the conventional spin valve.
The magnetoresistance effect element of the eighth to eleventh aspects of the invention is not limited to the embodiment described above. Rather, the element may be one which is formed by alternately stacking nonmagnetic films and ferromagnetic films, a number of times.
The ninth aspect of the present invention provides a magnetoresistance effect element comprising a stacked film on a substrate by sequentially stacking a magnetization-locked film which magnetization substantially can not rotate by a single magnetic field, nonmagnetic film and a filed-detecting film which detects a signal by the change in a magnetization based on the signal magnetic field, wherein, when said signal magnetic field has no intensity, each of the magnetization direction of said magnetization-locked film and said field-detecting film is substantially perpendicular to each other, and a sense current is made to flow in a direction which is substantially identical to the direction of the signal magnetic field.
In the ninth aspect of the invention, the magnetization of the antiferromagnetic film may be locked in various methods. Among these methods are: method of forming the film on the magnetization-clocked film in exchange-coupled connection; method of increasing the Hc value; and method of forming a high-Hc ferromagnetic on the magnetization-locked film. One of two alternative methods may be used to make the magnetization directions of two magnetic films intersect with each other. The first method is to impart an easy axis of magnetization to the magnetic-field detecting magnetic film, which intersects with the magnetization direction of the magnetization-locked film. The second method is to apply a small exchange-coupled bias (e.g., 5 kA/m or less) in the direction at right angles to the magnetization direction of the magnetization-locked film. In the second method, it is preferable, for CoFe films with larger anisotropy field, that the easy axis of the magnetic field detecting film exists in the almost same direction of the magnetization of the magnetization-locked film and the bias field to the magnetic field detecting film is slightly larger than the anisotropy field of the magnetic field detecting film. The second method is useful to enhance the magnetic permeability of CoFe with larger anisotropy field.
The tenth aspect of the present invention provides a magnetoresistance effect element comprising a bias film formed on a substrate, a first ferromagnetic film formed on the bias film to serve as a magnetization-locked film, a nonmagnetic film formed on the first ferromagnetic film, and a second ferromagnetic film formed on the nonmagnetic film to serve as a field detecting film, wherein the magnetization of the first ferromagnetic film is locked, and an angle xcex8 defined between the magnetization direction of the first ferromagnetic film and the magnetization direction of the second ferromagnetic film at nearly 0 signal field is 30xc2x0 to 60xc2x0. The first ferromagnetic film may serve as a field detecting film, and the second ferromagnetic film may serve as a magnetization-locked film by replacing the bias film on the second ferromagnetic film.
As the magnetization locking means in the tenth invention, there is a method in which an exchange bias produced by stacking an antiferromagnetic film onto a ferromagnetic film for locking magnetization or a ferromagnetic film is used as a high-coercive-force film. The means for inclining the magnetization direction of the other ferromagnetic film for signal magnetic field detection from the magnetization locking direction can be selected from a method using the axis of easy magnetization, application of a bias magnetic field from a hard from a hard magnetic film adjacent to the ferromagnetic film for signal magnetic field detection, a static magnetic bias generated by a ferromagnetic film stacked on the antiferromagnetic film for magnetization locking, and a current magnetic field from a sense current. The angle of inclination is preferably 30xc2x0 to 60xc2x0. To use the magnetic field from the field sense current, it is required to flow the sense current in substantially the same direction as the signal magnetic field. Note that in order to stabilize the magnetization locking direction, the sense current is desirably flowed such that the magnetic field from the sense current is applied in substantially the same direction as the magnetization locking ferromagnetic film.
The eleventh aspect of the present invention provides a magnetoresistance effect element comprising a stacked film formed on a substrate and constituted by (ferromagnetic film/nonmagnetic film), and at least two bias films layered on the uppermost ferromagnetic film in the stacked film and/or under the lowermost ferromagnetic film in the stacked film, wherein a bias magnetic field for the purpose of magnetization-locking is applied to at least one ferromagnetic film, a minimum bias magnetic field required for the purpose of disappearance of a magnetic domain is applied to at least one ferromagnetic film.
In the eleventh aspect, a bias magnetic field generated by some there means may be applied to the particular ferromagnetic film in a direction almost perpendicular to the above bias magnetic field. The ferromagnetic film applied with the bias magnetic field generated by that other means need not have an easy axis of magnetization.
In the eleventh aspect, the bias films may be formed on uppermost ferromagnetic film of the stacked film and between the substrate and the lowermost ferromagnetic film of the stacked film, respectively. Alternatively, the bias films may be formed on uppermost ferromagnetic film or between the substrate and the lowermost ferromagnetic film.
In the eleventh aspect of the invention, it is preferable that the axis of the bias magnetic field and the axis of each magnetization of the ferromagnetic film applied with the bias magnetic field intersect at substantially right angles. Hence, it is possible to enhance the magnetic permeability (xcexc) of the Co-based alloy film having high Hk.
As the bias magnetic field in this eleventh invention, it is possible to use at least one type of a bias magnetic field selected from the group consisting of an exchange coupled magnetic field from an antiferromagnetic film, an exchange coupled magnetic field or a static coupled magnetic field from a ferromagnetic film, and a current magnetic field.
As a method of generating the exchange coupled magnetic field, a method in which a ferromagnetic film is used as the bias film, and a film which is made to reduce an exchange bias is formed between a ferromagnetic film of the stacked film and the bias film, or a method in which a ferromagnetic film is used as the bias film, and the bias film is directly formed on a ferromagnetic film of the stacked film, may be used. In the former case, it is preferable that a uniaxial magnetic anisotropy (Hk) of the bias film is larger than that of the ferromagnetic film of the stacked film, and that a coercive force (Hc) of the bias film is larger than that of the ferromagnetic film of the stacked film.
In the eleventh aspect, a bias magnetic field by which the magnetization is essentially not moved by a signal magnetic field is applied to one of the uppermost and lowermost ferromagnetic films, and a magnetic field by which a signal magnetic field can be detected and Barkhausen noise can be removed is applied to the other. Stacking of the antiferromagnetic film is suitable for application of the former bias magnetic field. Stacking of the second ferromagnetic film or the antiferromagnetic film is suitable for application of the latter bias magnetic field. Examples of the second ferromagnetic film are a high-resistance soft magnetic film which is given a single domain by some method and in which the magnetization directions are aligned in one direction (e.g., a Co-based amorphous film heat-treated in a rotating magnetic field), a film with a high uniaxial magnetic anisotropy (e.g., a Co(Fe)-based amorphous film heat-treated in a static magnetic field), and a high-coercive-force film. A high-resistance soft magnetic film with a single domain can be realized by widening the second ferromagnetic film to be larger than the other films and stacking a hard magnetic film or an antiferromagnetic film onto the edge portion of the widened film.
The twelfth aspect of the present invention provides a magnetoresistance effect element comprising a stacked film formed on a substrate by alternately stacking at least three ferromagnetic films and at least two nonmagnetic films, wherein the magnetic permeabilities of the uppermost and lowermost ferromagnetic films serving as magnetization-locked films are lower than those of the other ferromagnetic films serving as field detecting films.
In the twelfth aspect, the method of decreasing the magnetic permeabilities of the uppermost and lowermost ferromagnetic films, i.e., the method of locking the magnetizations can be selected from a method using an antiferromagnetic film, a method using a hard magnetic film, and a method using a demagnetizing field, like in the eighth invention.
The thirteenth aspect of the present invention provides a magnetoresistance effect element comprising a magnetoresistance effect element including a high-coercive-force film in which a hexagonal C axis is present in the film surface, and a ferromagnetic film having a coercive force lower than that of the high-coercive-force film.
In the thirteenth aspect, the high-coercive-force film can also be used as film for applying a bias magnetic field. In addition, high-coercive-force films and intermediate films can be stacked a plurality of number of times.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims.